(a) Field of the Invention
The present invention relates to a thin film transistor (“TFT”) array panel, a liquid crystal display (“LCD”) having the TFT array panel, and a method thereof, and more particularly the present invention relates to a TFT array panel having a transflective TFT, an LCD including the TFT array panel, and a method of operating the LCD.
(b) Description of the Related Art
LCDs are one of the most widely used flat panel displays. An LCD includes a liquid crystal (“LC”) layer interposed between two panels each provided with field-generating electrodes. The LCD displays images by applying voltages to the field-generating electrodes to generate an electric field in the LC layer that determines orientations of LC molecules in the LC layer to adjust polarization of incident light. The light having adjusted polarization is either intercepted or allowed to pass by a polarizing film, thereby displaying images.
Depending on the light sources employed by the LCD, LCDs are classified as a transmissive LCD and a reflective LCD. The light source of the transmissive LCD is a backlight, and the light source of the reflective LCD is an external light. The reflective type of LCD is usually applied to a small or mid size display device.
A transflective LCD has been under development. The transflective LCD uses both a backlight and an external light as the light sources depending on circumstances, and are usually applied to small or mid size display devices. The transflective LCD includes a transmissive region and a reflective region in a pixel. While light passes through an LC layer only once in the transmissive region, light passes through the LC layer twice in the reflective region. Accordingly, gamma curves of the transmissive region and the reflective region are not coincident, and images are displayed differently between the transmissive region and the reflective region.
To solve this problem, the LC layer may be formed to have different thicknesses (cell gaps) between the transmissive region and the reflective region. Alternatively, the transflective LCD may be driven by two different driving voltages depending on whether the LCD is in a transmissive mode or a reflective mode.
However, when the two cell gap structure is applied, a thicker layer is required to be formed on the reflective region, thereby complicating the manufacturing process. Furthermore, since a high step is formed between the transmissive region and the reflective region, the LC molecules are aligned in a disorderly manner around the high step, thereby causing disclination in an image. Also, brightness reversion may occur in a high voltage range. On the other hand, when the method using two different driving voltages is applied, gamma curves cannot be coincident due to the inconsistency between critical voltages for transmissive brightness and reflective brightness.